Śatapatha Brāhmaṇa ("of a hundred paths") 5.4.3.5

5.4.3.5

tamantarvedyabhyavavartya yunakti | mitrāvaruṇayostvā praśāstroḥ praśiṣā yunajmīti bāhū vai mitrāvaruṇau bāhubhyāṃ vai rājanyo maitrāvaruṇastasmādāha mitrāvaruṇayostvā praśāstroḥ praśiṣā yunajmīti

Having turned it (so as to stand) inside the Vedi, he yokes it with, 'I yoke thee by the direction of Mitra and Varuna, the directors;' for Mitra and Varuna are the two arms, and by his arms the Râganya belongs to Mitra and Varuna that is why he says, 'I yoke thee by direction of Mitra and Varuna, the directors.'